1. Field of the Invention
The present invention relates to a method for manufacturing an X-ray detector for detecting X-ray and the X-ray detector manufactured thereby.
2. Description of the Related Art
A flat X-ray detector using an active matrix has been attracting attention as a new-generation X-ray diagnostic image detector. In this type of the X-ray detector, when X-ray is irradiated on an object, an X-ray photographed image or a real-time X-ray image of the object is output as digital image signals. Since the X-ray detector is a solid detector, it is extremely expected in terms of image quality performance and stability so that a great amount of research and development has been progressed.
As the first use of practical application, such X-ray detector has been developed and commercialized recently for photographing a chest region or a general purpose photograph in order to collect still images with the use of a comparatively large dose. Commercialization of such X-ray detector is expected in immediate future for applications in fields of circulatory organs and digestive organs in which the realization of a real-time moving image having a higher performance and displayed by thirty or more frames per second under the fluoroscopy dose is required. In the use application of such moving image, improvements in S/N ratio, a real-time processing technology for very small signals and the like are important items to be developed.
In the meantime, X-ray detectors are classified broadly into two types of technique, i.e. a direct technique and an indirect technique. The direct technique is such that X-ray is converted directly into electric charge signals by means of a photoconducting film such as a-Se, and the signals are guided to a capacitor for accumulating electric charge. In the direct technique, since the photoconductive electric charge produced by the X-ray is guided directly to the capacitor for accumulating electric charge due to a high electric field, the resolution characteristic defined substantially by pitches of the picture electrodes of an active matrix is obtained. On the other hand, the indirect technique is such that X-ray is once converted into a visible light with a scintillator layer, and the visible light is converted into signal electric charges by means of a photoelectric transducer such as an a-Si photodiode and a CCD to guide the signal electric charges to a capacitor for accumulating electric charge. Accordingly, degradation arises in the resolution characteristic due to optical diffusion and scattering appearing before the visible light from the scintillator layer reaches the photodiode or the CCD.
In the X-ray detector of the indirect technique generally, the characteristics of a scintillator layer become important from the structural point of view. In order to elevate the output signal intensity with respect to the X-ray input, there are many cases in which a high-luminance fluorescent material composed of, for example, a halide such as cesium iodide (CsI) or an oxide-based compound such as sulfated gadolinium (GOS) is used for the scintillator layer. Furthermore, there are generally many cases in which a high-density scintillator layer is formed uniformly on a circuit board on which a plurality of photoelectric transducers have been provided in accordance with a vapor growth method such as vacuum deposition method, sputtering technique, and CVD method.
However, when a halide such as CsI being a high-luminance fluorescent material is used in the scintillator layer, since the reactivity of a halogen element such as iodine is high, the halide reacts with an electropositive element in the photoelectric transducer being in contact with the scintillator layer, and the halide reacts with the moisture in the atmospheric air, whereby the scintillator layer deliquesces. As a result, there arise problems of degradations in a variety of characteristics and the reliability of an X-ray detector, decrease in the productivity and increase in the production cost of such X-ray detector.
In this connection, an X-ray detector of the indirect technique intends to form a uniform scintillator layer in which a transparent layer of polyimide is formed on the surface of a circuit board on which photoelectric transducers have been arrayed, and a scintillator layer is formed on the transparent layer, whereby corrosion of the photoelectric transducers is prevented. In addition, a protective layer of polyparaxylilene for covering the scintillator layer to seal it closely is provided, whereby the scintillator layer is protected against the deliquescence due to the moisture in the atmospheric air (e.g. Jpn. Pat. Appln. KOKAI Publication No. 2002-48872 (page 3, FIGS. 1-3)).
However, since the peripheral part of the protective layer covering the scintillator layer is joined to a circuit board or the like made of a different material, there still remain such problems that a joint strength in the interface of the protective layer and a member made of a different material decreases easily, and further that the protective layer exfoliates due to a stress generated by a difference in coefficients of thermal expansion between the protective layer and the member made of the different material, whereby sealing property of the scintillator layer is damaged.